Tear the rosettes from the broccoli head and put them in the pot with more water. The amount of water you use is up to you, depending on how thick you prefer your cream soup. I like to add about another 3 1/5 cups (750 ml). Leave it to boil another 10 min.
Take the pot off the stove to cool. Blend the mixture in a blender or with a hand blender. Add salt and black pepper to taste, as well as 4 tbsp cream and return to the stove for 5 min.
After serving in a bowl/plate, squeeze in the juice from a slice of lemon and add the croutons on top.